The present invention relates to a seal and an electrochemical fuel cell including the seal. Especially, the seal in the electrochemical fuel cell prevents fluid which is provided in a space from leaking. Furthermore, the seal is provided in the electrochemical fuel cell for sealing a space between an electrolyte membrane and a separator or for sealing a coolant path between two separators.
In an electrochemical fuel cell, uniting a generator part and a frame part as one body by a hot-press method is proposed, as a sealing method which seals a path shaped by an electrolyte membrane and a separator for a fuel gas containing hydrogen or an oxidative gas containing oxygen. Two electrodes sandwich the electrolyte membrane in the generator part, and an opening area of the frame is marginally smaller than one of the generator parts made of plastic. One of these examples is disclosed in Japanese Laid-Open Patent Application No. 10-199551. Moreover, in the above-mentioned method, the path shaped by the electrolyte membrane and the separator for the fuel gas or the oxidative gas is sealed by providing a seal such as an O-ring between the frame part and the separator.
As another method, a method in which the generator part and the separator are connected by using adhesives is also proposed. In this method, the adhesives function as a comparatively soft seal after the connection, and the adhesives seal the path for the fuel gas or the oxidative gas.
In the aforementioned methods, which unite the generator part and the frame part as one body and furthermore puts the seal between the frame and the separator, sealing ability on the sealing surface could not be secured, because a clearance between the frame and the separator varies by a thermal expansion caused by heat of the electrolyte membrane in the generator part.
Furthermore, in the above-mentioned method which uses the adhesives, when a fuel cell stack is assembled by stacking a plurality of the generators and the separators, a stiffness of the fuel cell stack is weakened by laminating sealing parts using adhesives. Consequently, the fuel cell stack can not have sufficient stiffness and rigidity.
It is thus one object of the present invention to solve the aforementioned problems. Another object of the invention is to provide a seal which can seal securely by following and responding to a varying length of an electrolyte membrane or a separator. Furthermore, an object of the invention is to provide a fuel cell stack which has a sufficient stiffness, when a plurality of electrolyte membranes, separators, etc. are stacked in laminated condition.
According to one aspect of the invention, a seal has at least two layers with different coefficients of elasticity. As the first embodiment of a seal in an electrochemical fuel cell, a seal includes a first layer and a second layer having different coefficients of elasticity, and the seal prevents fluid in a space from leaking. For example, the seal is made of rubber, and the rubber hardness of the harder layer is 60 degrees or higher and the softer layer is 60 degrees or lower.
Since the coefficients of elasticity of the layers in the seal are different, the seal can appropriately respond to two members which sandwich the seal, and the seal can seal sufficiently even if one of the two members or two members change its length or both lengths. Providing the layers with different coefficients of elasticity in series between the two members indicates that a softer layer and a harder layer are provided in the seal. Since the softer layer is provided in the seal, this softer layer can elastically deform by responding to the changing length of the one or two members. On the contrary, since the harder layer is provided in the seal, the other layer except the harder one changes the shape by elastic deformation, and the other layer can follow the changing length. The harder layer contributes to obtain a higher stiffness between the two members, because the harder layer has a higher resilience of elastic deformation. Consequently, the stiffness of the parts which uses the seal becomes higher, and an upper limit of the compression rate of the two members with the seal can be improved. At the same time, a high sealing performance of the seal can be obtained.
Incidentally, a seal containing three or more layers is also available, because above-mentioned results can be obtained by having at least two layers with different coefficients of elasticity.
When the softer layer is connected to one of the two members after the harder layer is connected to another member, the softer layer (that is, the lower coefficient of elasticity) absorbs a surface roughness of the one of the two members. Consequently, the higher sealing ability can be achieved.
The first embodiment of an electrochemical fuel cell is an electrochemical fuel cell including an electrolyte membrane, a first electrode on one side of the electrolyte membrane and a second electrode on another side of the electrolyte membrane, a first separator and a second separator sandwiching the first and second electrodes; and the above-mentioned seal between the electrolyte membrane and one of the first and second separators. The electrolyte membrane, two electrodes and two separators are stacked in the lamination condition. This electrochemical fuel cell has a good performance of a sealing ability, and a high stiffness of the fuel cell stack is obtained, because it provides the first embodiment seal for the seal. The total performance and reliability of the fuel cell, then, can be improved.
In this first embodiment of the fuel cell, it is also available that the layer with a higher coefficient of elasticity is positioned to face the electrolyte membrane and the layer with a lower coefficient of elasticity is positioned to face the separator. Since the layer having a lower coefficient of elasticity absorbs the surface roughness of the separator in this case, a higher sealing performance can be secured.
In the first embodiment of the fuel cell, the above-mentioned seal of the first embodiment of the seal can be provided for sealing a coolant path between the first separator and the second separator.
As the same reason of the first above-mentioned embodiment of the fuel cell including the seal, the first embodiment of the fuel cell including the seal for sealing the coolant path has a high sealing ability and a high stiffness of the fuel cell stack in the lamination direction. The performance and the reliability of the fuel cell can be improved.
As the second embodiment of a seal in an electrochemical fuel cell, a seal includes a base part and a seal part. The base part has a first surface, a second surface, and a third surface. The second and third surfaces are opposite to the first surface, and the third surface is closer to the first surface than the second surface. The seal part on the third surface of the base part extends beyond a plane defined by the second surface of the base part. The coefficient of elasticity of the base part is higher than the coefficient of elasticity of the seal part. For example, the seal is made of rubber, and the rubber hardness of the base part is 60 degrees or higher and the rubber hardness of the seal part is 60 degrees or lower.
In this second embodiment of the seal, since the seal part is comparatively soft, by the elastic deformation the seal part can follow the length of the members which sandwiches the seal, though the length changes due to a heat expansion. When the seal part is connected to one of the members after the base part is connected to another member, the seal part having the lower coefficient of elasticity absorbs a surface roughness of the one of the members. Consequently, the higher sealing ability can be He attained. Moreover, since the base part has a high resilience against deformation, the stiffness in the pressure direction can be improved. Especially, if the base and seal parts are made up so that the base part receives a pressure from the members when the seal receives an excessive pressure than a predetermined value, the higher stiffness in the pressure direction can be obtained.
The second embodiment of an electrochemical fuel cell is attained by providing the above-mentioned second embodiment of the seal as a seal to the same type of the fuel cell as the first embodiment. A high sealing ability and high stiffness of the fuel cell stack are obtained as the same as the first embodiment of the fuel cell. Accordingly, the performance and reliability of the fuel cell can be improved.
In the second embodiment of the electrochemical fuel cell, the fuel cell can also be designed so that the base part receives a pressure from the separator and the seal part receives a pressure from the electrolyte membrane and the base part. The high stiffness of the fuel cell stack and high sealing ability can be achieved by this fuel cell.
In the second embodiment of the fuel cell, the above-mentioned seal of the second embodiment of the seal can not only be provided to a seal between an electrolyte membrane and a separator, but can also be provided as a seal which seals a coolant path between the separators.
As the third embodiment of a seal in an electrochemical fuel cell, a seal includes a base part and a seal part. The base part has a first surface, a second surface, a third surface, and a fourth surface. The first surface is opposite to the second surface, and the third surface is opposite to the fourth surface. The distance between the first and second surfaces is greater than the distance between the third and fourth surfaces. The seal part on the third and fourth surfaces extends beyond a plane defined by the first and/or the second surface. Furthermore, the coefficient of elasticity of the base part is higher than the coefficient of elasticity of the seal part.
In this seal, since the seal part has a comparatively soft seal part, by the elastic deformation the seal part can follow the length of the members which sandwiches the seal, though the length changes due to a heat expansion. Accordingly, the higher sealing ability can be attained. Moreover, since the base part has a high resilience against deformation, the stiffness in the pressure direction can be obtained, in the same way as the second embodiment of the seal.
The third embodiment of an electrochemical fuel cell is attained by providing the above-mentioned third embodiment of the seal to the same type fuel cell of the first or second embodiment. By assembling the fuel cell high sealing ability and high stiffness of the fuel cell stack are obtained as the same as the first or second embodiment. Accordingly, the performance and reliability of the fuel cell can be improved.
In the third embodiment of the fuel cell, the above-mentioned seal of the third embodiment of the seal can not only be provided as a seal between an electrolyte membrane and a separator, but can also be provided as a seal which seals a coolant path between the separators.
As the fourth embodiment of a seal in an electrochemical fuel cell, a seal has a first side with a substantially plane surface and a second side with a first sealing member and a second distinct sealing member. The cross-sectional area of the second sealing member is less than the cross-sectional area of the first sealing member. The second sealing member is substantially half elliptical in cross-section. It is also available that a cross-sectional shape of the second sealing member is substantially half circular, trapezoidal or rectangular. It is also available that the second sealing member is substantially extends above the plane defined by the first sealing.
In the fourth embodiment of a seal, since the smaller and extending area of the seal receives a greater stress, it elastically deforms more largely and the seal ability is secured. Since the larger area of the seal receives a lower stress than the smaller area, the elastic deformation of the larger area is smaller and a high stiffness in the direction of the pressure is secured. The high sealing ability and the stiffness is, then, obtained.
The fourth embodiment of an electrochemical fuel cell is achieved by providing the above-mentioned fourth embodiment of the seal as a seal to the same type of the fuel cell as the first, second or third embodiment.
In the fourth embodiment of the fuel cell, the above-mentioned seal of the fourth embodiment of the seal can be adopted to a seal part which seals a coolant path shaped by the separators.
By this fuel cell a high sealing ability and a high stiffness of the fuel cell stack are obtained as the same as the first, second, or third embodiment. Consequently, the performance and reliability of the fuel cell can be achieved.